Luke 21:5 And as some spake of the temple, how it was adorned with goodly stones and gifts, he said, Luke 21:6 As for these things which ye behold, the days will come, in the which there shall not be left one stone upon another, that shall not be thrown down.
This was the temple built by Herod's order. It was 400 yards wide and 500 yards long. The outside was plated with gold, so that it glistened in the sunlight. Other parts of the temple were made of white marble.
Later in the century, Rome came against the rebels in Jerusalem. Many fled to the temple. A drunken soldier set fire to the temple. The gold leaf melted and went into the cracks of the temple stones. The Romans tore the temple apart, stone by stone to get the gold in the cracks.
Luke 21:7 And they asked him, saying, Master, but when shall these things be? and what sign will there be when these things shall come to pass? Luke 21:8 And he said, Take heed that ye be not deceived: for many shall come in my name, saying, I am Christ; and the time draweth near: go ye not therefore after them.
Beware of false Christs, it shows the time is near: do not follow them. False Christs and false teachers are a sign of the end times. When Jesus comes it will not be by hearsay.
Rev 1:7 Behold, he cometh with clouds; and every eye shall see him, and they also which pierced him: and all kindreds of the earth shall wail because of him. Even so, Amen.